As known vapor compression refrigeration cycles that use a refrigerant such as carbon dioxide (CO2) in its supercritical region, there is a vapor compression refrigeration cycle in which a refrigerant that has flowed out of a radiator is branched such that one portion of the refrigerant is subjected to pressure reduction in a pressure reducing device, flows through a cooler so as to exchange heat with the other portion of the refrigerant that has flowed out of the radiator, and is injected in the middle of a compression stroke of a compressor (see Patent Literature 1, for example). The vapor compression refrigeration cycle disclosed in Patent Literature 1 increases the refrigeration capacity by reducing the specific enthalpy of the other portion of the refrigerant. Further, the pressure reducing device is configured to increase the opening degree thereof when the degree of superheat of the one portion of the refrigerant at the outlet of the cooler is higher than a predetermined degree of superheat.